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Abstract: Microemulsions are potential drug
carrier systems for oral, topical, and parenteral
administration. They offer the advantage of spontaneous
formation, ease of manufacturing and scale-up,
thermodynamic stability, and improved drug
solubilization and bioavailability. Preparing a
pharmaceutically acceptable dosage form demands a clear
understanding of the micro-emulsion structure, phase
behavior, factors leading to its thermodynamic
stability, factors influencing drug release from the
formulation, requirements of ideal microemulsion
excipients, and the potential uses and limitations of
the microemulsion system. Knowledge of the various
methods available to thoroughly characterize a
microemulsion system is essential. An overview of these
factors is presented in this review. While microemulsion
is used in several fields, in this review the
pharmaceutical applications are emphasized. The review
is written so that a newcomer to the field can easily
grasp the important facts pertaining to this novel
delivery system.
Introduction
The term "Microemulsion" refers to a thermodynamically
stable isotropically clear dispersion of two immiscible
liquids, such as oil and water, stabilized by an
interfacial film of surfactant molecules. A
microemulsion is considered to be a thermodynamically or
kinetically stable liquid dispersion of an oil phase and
a water phase, in combination with a surfactant. The
dispersed phase typically comprises small particles or
droplets, with a size range of 5 nm-200 nm, and has very
low oil/water interfacial tension. Because the droplet
size is less than 25% of the wavelength of visible
light, microemulsions are transparent. The microemulsion
is formed readily and sometimes spontaneously, generally
without high-energy input. In many cases a co surfactant
or co solvent is used in addition to the surfactant, the
oil phase and the water phase.
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